Despite the availability of mechanical picking aids to increase picker productivity, manual labor remains the dominant method of picking citrus and similar tree crops. Efforts at replacing traditional methods with mass removal mechanical systems have been slow, primarily because their economic justification under current labor conditions continues to be questionable. See, J. Whitney & R. Harrell, "Status of Citrus Harvesting in Florida," 42 J. Agric. Eng'g. Res. 285-299 (1989). For deciduous crops, the use of abscission chemicals to loosen the fruit has been tried to make mechanical harvesting more efficient. However, because chemical fruit loosening causes considerable preharvest drop, systems were developed to remove fruit to the ground and to pick up mechanically. Id. at 291. This has led to problems with fruit quality.
For processed fruit, the main concerns relate to contamination picked up from the soil. In addition to sand that has to be removed from fruit which has contacted the ground, there is concern about microflora which penetrate abraded skin and cause a decay problem, especially in unpasteurized juice. The decay level is about three times as high on ground fruit as for fruit which is hand-picked and placed in the bag. "Citrus Harvesting--How Can It Be Improved?," Florida Grover and Rancher 10.
Past approaches to tree crop harvesting systems include the use of limb, air or trunk shakers to shake the trees to remove fruit to the ground, with or without the aid of chemicals, followed by the use of machines to gather, pick up and load the dropped fruit. Examples of such systems are disclosed in U.S. Pat. Nos. 4,435,950 and 4,199,913. Use of trunk shakers has been limited for citrus in some instances, however, because of poor fruit removal, undesirable bark damage, and inadequate tree trunk height for good shaker clamp attachment. See, S. Heddon, et al., "Trunk Shakers for Citrus Harvesting--II: Tree Growth, Fruit Yield and Removal," 4(2) Applied Eng'g in Agriculture 102 (June 1988). Limb and air shakers do not have the same bark removal and trunk height problems, but may cause limb damage. Of particular concern, also, is the fact that shakers are nondiscriminatory, so may cause unacceptable damage to the next year's crop.
Various mechanical separating devices which contact the fruit itself have been tried. One approach uses a bank of flexible, rotating augers inserted into the tree canopy to twist and pull the fruit out of the tree. Another utilizes a soft, gummy rotating cuff attached to the end of a hollow lightweight vacuum tube. The vacuum pulls the fruit into contact with the cuff, which spins to separate the fruit from the tree. The fruit is then sucked through a central hole and into the tube for gathering.
The Pic-Rig.TM. mechanical citrus picker, marketed by Agricultural Machine Inc., Sebring, Fla., has a bank of bars with picking hooks that extend into the tree canopy, and pull fruit off when they retract. To prevent branch damage, spring tension on the hooks releases them when they meet resistance. The Mongoose.TM. B-300 picker, marketed by Mongoose Harvesting Systems, Arcadia, Fla., consists of a round basket mounted on the end of a citrus highlift. A curved rod rotates inside the top of the basket to remove fruit caught in openings of a protective cage. The picked fruit collects in the bottom of the basket which opens like a clam shell for emptying.
Other relevant background is given in U.S. Pat. Nos. 3,704,576; 5,205,121; 4,435,950; 4,199,913; and 4,228,870.
U.S. Pat. No. 3,704,576 discloses a machine for picking up fruit after it has been stripped from the tree. The fruit is transported to a waiting truck for transport to a distribution point. U.S. Pat. No. 5,205,121 discloses a complex method of vacuum and human manipulation of screens for extracting fruit from trees. Fruit is collected in netting, then packaged and transported to a distribution center in a complicated and slow harvesting process. U.S. Pat. No. 4,435,950 discloses a complicated arrangement of spoked extrusions which are used to part tree branches for picking. Tree height limitations would, however, make this approach impractical for harvesting citrus fruits. U.S. Pat. No. 4,199,913 discloses a system wherein a machine is used to grade fruit by size, before loading and transporting the fruit to the distribution center. And, U.S. Pat. No. 4,228,870 discloses a system of platforms which surround the tree, to provide walking surfaces for the harvesters. The pickers stand on the platforms, and pick the fruit.